The long-term goal of this proposal is to improve the cytotoxic and radiosensitizing efficacy of cancer gene therapy using the cytosine deaminase/5FC (CD/5FC) enzyme/prodrug strategy. In this renewal application, we propose to increase the effectiveness of yCD gene therapy based on two discoveries made during the previous funding period. Specific Aim 1 is to optimize expression of yCD though the use of ionizing radiation as a method of increasing gene transfer in vitro and in vivo. Our preliminary results show that radiation can significantly increase adenoviral-mediated gene transfer in vitro and in vivo. We hypothesize that radiation can increase binding and uptake of adenovirus leading to increased transgene expression. Specific Aim 2 is to optimize expression of yCD though development of an enhanced CEA promoter. In the preliminary results, we demonstrate the development of an active construct that produces yCD selectively in CEA expressing cells at a level equal to or greater than that achieved with strong, non-specific promoters. We propose to improve this promoter/enhancer and to increase the uptake of this improved vector with radiation. We hypothesize that the increase in yCD expression due to the increase in adenoviral uptake produced by radiation can be further increased and better targeted to tumors by using adenovirus-containing yCD under control of this CEA promoter/enhancer. In Specific Aim 3 we propose to carry out therapy experiments using a novel bioluminescence assay that permits us to non-invasively measure tumor size. Our clinical expertise in high dose conformal radiation for liver tumors as well as other organs will be directly applicable to these improvements in our gene therapy approach, and will permit us to develop an effective gene therapy program for intrahepatic and systemic cancer based on chemoradiation.